Fabricating method and fabricating apparatus for secondary battery

ABSTRACT

To provide a fabricating method and a fabricating apparatus for a lithium-ion secondary battery having stable charge characteristics and lifetime characteristics. A positive electrode is subjected to an electrochemical reaction in a large amount of electrolytic solution in advance before a secondary battery is completed. In this manner, the positive electrode can have stability. The use of the positive electrode enables fabrication of a highly reliable secondary battery. Similarly, a negative electrode is subjected to an electrochemical reaction in a large amount of electrolytic solution in advance. The use of the negative electrode enables fabrication of a highly reliable secondary battery.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an object, a method, or a manufacturingmethod. The present invention relates to a process, a machine,manufacture, or a composition of matter. One embodiment of the presentinvention relates to a semiconductor device, a display device, alight-emitting device, a power storage device, a driving methodtherefor, or a manufacturing method therefor. In particular, oneembodiment of the present invention relates to a fabricating apparatusfor a secondary battery.

Note that electronic devices in this specification mean all devicesincluding secondary batteries, and electro-optical devices includingsecondary batteries, information terminal devices including secondarybatteries, vehicles including secondary batteries, and the like are allelectronic devices.

2. Description of the Related Art

In recent years, portable information terminals typified by smartphoneshave been actively developed. Portable information terminals, which area kind of electronic devices, are desired to be lightweight and compactby users.

Patent Document 1 discloses an example of a hands-free wearable devicewith which information can be visually obtained anywhere, specifically,a google-type display device that includes a CPU and is capable of datacommunication. The device disclosed in Patent Document 1 is also a kindof electronic device.

Most wearable devices and portable information terminals includesecondary batteries (also referred to as batteries) that can berepeatedly charged and discharged, and have problems in that there is alimitation on the time for operation of the wearable devices and theportable information terminals because their light weight andcompactness limit the battery capacity. Secondary batteries used inwearable devices and portable information terminals should belightweight and should be able to be used for a long time.

Examples of secondary batteries include a nickel-metal hydride batteryand a lithium-ion secondary battery. In particular, lithium-ionsecondary batteries have been actively researched and developed becausethe capacity thereof can be increased and the size thereof can bereduced.

Electrodes serving as positive electrodes or negative electrodes oflithium-ion secondary batteries are each formed using, for example,metal lithium, a carbon-based material, or an alloy-based material.Lithium-ion secondary batteries are divided into lithium metalbatteries, lithium-ion secondary batteries, and lithium polymersecondary batteries according to the kind of electrolyte. Furthermore,batteries are divided into thin (laminated) batteries, cylindricalbatteries, coin-type batteries, and rectangular batteries according tothe kind of an exterior material in which electrodes and an electrolyteare packed.

Patent Document 2 discloses a fabricating method for a lithium-ionsecondary battery that improves cycle performance by using analloy-based material (e.g., silicon) with increased reactivity withlithium for a negative electrode active material.

REFERENCE

[Patent Document 1] Japanese Published Patent Application No.2005-157317

[Patent Document 2] Japanese Published Patent Application No. 2013-69418

SUMMARY OF THE INVENTION

A lithium-ion secondary battery using an electrolytic solution isfabricated by surrounding a positive electrode (e.g., alithium-containing oxide material), a negative electrode (e.g., carbon),and another member with an exterior material, introducing theelectrolytic solution in a surrounded region, and sealing the exteriormaterial. After that, the fabricated lithium-ion secondary battery issubjected to the first charge. Alternatively, before sealing, the firstcharge is performed.

In the first charge, which is also called the initial charge, a chemicalreaction might occur at the interface with an electrode and/or theinterface with an electrolytic solution, generating a gas. Furthermore,lithium ions released from a lithium-containing oxide material aretransferred to and inserted into a negative electrode. When lithiumreacts with carbon in the negative electrode at this time, a thin filmof Li₂O or the like is formed on a surface of carbon. This thin filmmight affect the transfer of lithium ions and the like, leading to achange in the characteristics of a battery.

A fabricating method and a fabricating apparatus for a lithium-ionsecondary battery having stable charge characteristics and lifetimecharacteristics are provided.

An object of one embodiment of the present invention is to provide anovel power storage device, a novel secondary battery, or the like. Notethat the descriptions of these objects do not disturb the existence ofother objects. In one embodiment of the present invention, there is noneed to achieve all the objects. Other objects will be apparent from andcan be derived from the descriptions of the specification, the drawings,the claims, and the like.

In view of the above, during fabrication of a secondary battery, apositive electrode is subjected to an electrochemical reaction in anabundance of electrolytic solution to sufficiently form a reactionproduct in advance, typically generate a gas. Then, the secondarybattery is fabricated using the positive electrode.

Not only in the initial charge, but whenever a gas is generated in asecondary battery, a sealed region expands and thus the secondarybattery expands, which might degrade the characteristics of the battery.

A positive electrode is subjected to an electrochemical reaction in alarge amount of electrolytic solution in advance before a secondarybattery is completed. In this manner, the positive electrode can havestability. The use of the positive electrode enables fabrication of ahighly reliable secondary battery. The initial charge also changes partof the quality of the large amount of electrolytic solution. Not thislarge amount of electrolytic solution containing the reaction productbut a small amount of electrolytic solution prepared separately is usedin fabricating a secondary battery. The positive electrode subjected tothe initial charge is unlikely to react with the small amount ofelectrolytic solution and hardly form a reaction product.

Like the positive electrode, a negative electrode is subjected to anelectrochemical reaction in an electrolytic solution before thesecondary battery is completed, whereby the negative electrode can havestability.

A fabricating apparatus for a secondary battery disclosed in thisspecification includes a container, an electrolytic solution in thecontainer, a first electrode for an electrochemical reaction in theelectrolytic solution, a first cord electrically connected to the firstelectrode, and a second cord electrically connected to a secondelectrode including an active material layer. The first cord and thesecond cord are electrically connected to a device for controllingreduction conditions or oxidation conditions.

The fabricating apparatus further includes a means for stirring theelectrolytic solution in the container. Stirring can promote anelectrochemical reaction (oxidation or reduction) to reduce treatmenttime. The means for stirring the electrolytic solution in the containerincludes, for example, a pump that discharges an argon gas in the formof bubbles in the container of the fabricating apparatus. Alternatively,the means for stirring the electrolytic solution in the container may bea magnet stirrer, and a mechanism that rotates the magnet stirrer may beprovided at the bottom of the container.

Furthermore, to shorten treatment time by promotion of anelectrochemical reaction (oxidation or reduction), a means for heatingthe electrolytic solution in the container (e.g., a heater) may beprovided.

The fabricating apparatus further includes an exhaust means forexhausting a gas in the container. The exhaust means preferably exhaustsa gas from the hermetically-closed apparatus with the use of a fan. Forexample, the hermetically-closed apparatus is maintained at a pressureof approximately 0.5 atmospheres.

Alternatively, a batch-type apparatus may be employed to performtreatment on a plurality of electrodes. In that case, more than onesecond cord that is electrically connected to the second electrode isprovided so that more than one second electrode is subjected toreduction or oxidation at a time in the electrolytic solution in thefabricating apparatus.

A fabricating method for a secondary battery using an electrode formedwith the above fabricating apparatus for one or both of electrodes isalso one embodiment of the present invention. The fabricating method fora secondary battery includes the steps of forming a first electrodeincluding a positive electrode active material layer; forming a secondelectrode including a negative electrode active material layer;performing electrochemical reduction or oxidization on the firstelectrode or the second electrode put in an electrolytic solution in acontainer by supplying a current in the electrolytic solution with theelectrode used as one electrode; taking out the first electrode orsecond electrode that has been subjected to the electrochemical reactionfrom the electrolytic solution in the container and drying the firstelectrode or second electrode; packing a stack formed of the firstelectrode and the second electrode in a region surrounded by an exteriorbody having an opening; introducing the electrolytic solution in theregion surrounded by the exterior body; and closing the opening of theexterior body.

In the above fabricating method, the electrolytic solution containslithium, and the electrode subjected to the electrochemical reaction islithium foil.

The aforementioned fabricating apparatus can be efficiently used when amaterial with high irreversible capacity is used for a positiveelectrode or a negative electrode. Thus, the use of the fabricatingapparatus allows fabrication of a secondary battery that can be usedwith minimum wastage of a material for an electrode active material.

Here, reversible capacity and irreversible capacity will be describedbelow.

The standard electrode potential (equilibrium potential) of lithium isas very low as −3.045 V (vs. SHE) at which, for example, many organicsolvents are reduced and decomposed in a negative electrode. However, inthe case of some organic solvents, reductive decomposition allows adecomposition product to collect on a surface and form a film, whichinhibits further decomposition of the organic solvent. As the film isformed, the decomposition reaction of the electrolyte solution, which isan irreversible reaction, becomes less likely to occur than a reactionof lithium ions, which is a reversible reaction. Mainly during theinitial charge and discharge, an irreversible reaction occurs and causesmovement of electric charge, the amount of which equals the sum of thosein the reversible reaction and the irreversible reaction.

During the initial charge, in addition to the reversible reaction due torelease of lithium ions from a positive electrode, the irreversiblereaction occurs and the amount of moving electric charge increasesaccordingly. The amount of moving electric charge involved in theirreversible reaction is referred to as irreversible capacity, and theamount of moving electric charge involved in the reversible reaction isreferred to as reversible capacity. They collectively correspond to theinitial charge capacity.

In contrast, during the initial discharge, although the reversiblechemical reaction between lithium ions and the positive electrode occursand causes movement of electric charge, movement of electric chargeinvolved in the irreversible reaction does not occur. That is, thereversible capacity is the discharge capacity. Here, the ratio of thedischarge capacity to the charge capacity is referred to as charge anddischarge efficiency. Higher irreversible capacity means lower chargeand discharge efficiency.

A material for a positive electrode active material is a factor thatdetermines the irreversible capacity of the positive electrode and thuspreferably has low irreversible capacity and high charge and dischargeefficiency.

However, in many cases, as a material for a positive electrode activematerial has better cycle performance and higher capacity, itsirreversible capacity is relatively higher and its charge and dischargeefficiency is relatively lower. If a material having low charge anddischarge efficiency is used for a positive electrode active material,movement of electric charge corresponding to irreversible capacity inaddition to reversible capacity occurs during the initial charge. Here,in a battery reaction, the amount of electric charge in a positiveelectrode reaction is equal to the amount of electric charge in anegative electrode reaction. Hence, in a negative electrode, a largeramount of material for a negative electrode active material is neededbecause of the electric charge corresponding to the irreversiblecapacity in addition to the reversible capacity. This increases the massand volume of the negative electrode, leading to lower battery capacityper unit mass and volume. Additionally, the increased amount of materialfor negative electrode active material does not contribute to a batteryreaction during and after the second charge and discharge; this iswasteful of the material.

The same applies to a negative electrode. A high-capacity material for anegative electrode active material has relatively high irreversiblecapacity and low charge and discharge efficiency in many cases. Hence,in the case where a high-capacity material for a negative electrodeactive material is used in a negative electrode of a secondary battery,an extra amount of material for a positive electrode active materialwith capacity corresponding to the irreversible capacity is needed,since the amount of electric charge in a negative electrode reaction isequal to the amount of electric charge in a positive electrode reaction.This increases the mass and volume of the positive electrode, leading tolower battery capacity per unit mass and volume. The increased amount ofmaterial for a positive electrode active material does not contribute toa battery reaction; this is wasteful of the material.

One embodiment of the present invention can provide a secondary batteryhaving a high electrode capacity, high-speed charge and dischargecharacteristics, and improved cycle performance.

One embodiment of the present invention can provide a fabricatingapparatus and a fabricating method for a secondary battery having asmall initial capacity loss. Furthermore, a lithium-ion battery that isfabricated with the fabricating apparatus has high cycle performance.

One embodiment of the present invention can provide a novel electrode, anovel secondary battery, or a novel power storage device. Note that oneembodiment of the present invention is not limited to these effects.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIG. 1 is an example of a schematic cross-sectional view of afabricating apparatus of one embodiment of the present invention;

FIG. 2 is an example of a schematic cross-sectional view of afabricating apparatus of one embodiment of the present invention;

FIGS. 3A to 3F illustrate fabricating steps of a thin secondary batteryof one embodiment of the present invention;

FIGS. 4A and 4B illustrate coin-type secondary batteries, and FIG. 4Cillustrates a cylindrical secondary battery;

FIG. 5 is an example of a schematic cross-sectional view of afabricating apparatus of one embodiment of the present invention;

FIG. 6 is a photograph of a fabricating apparatus of one embodiment ofthe present invention;

FIG. 7A is a graph showing the charge and discharge characteristics of asecondary battery of one embodiment of the present invention, and FIG.7B is a graph showing the charge and discharge characteristics of asecondary battery of a comparative example;

FIGS. 8A to 8C show a charge/discharge test;

FIGS. 9A to 9D show a charge/discharge test; and

FIG. 10 shows a charge/discharge test.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments and examples of the present invention will be describedbelow in detail with reference to the drawings. However, the presentinvention is not limited to the descriptions below, and it is easilyunderstood by those skilled in the art that modes and details disclosedherein can be modified in various ways. Further, the present inventionis not construed as being limited to the descriptions of the embodimentsand the examples.

The term “electrically connected” includes the case where components areconnected through an “object having any electric function”. There is noparticular limitation on the “object having any electric function” aslong as electric signals can be transmitted and received between thecomponents connected through the object.

The position, size, range, or the like of each component illustrated indrawings and the like is not accurately represented in some cases forsimplification. Therefore, the disclosed invention is not necessarilylimited to the position, size, range, or the like disclosed in thedrawings and the like.

The ordinal number such as “first”, “second”, and “third” are used toavoid confusion among components.

(Embodiment 1)

In this embodiment, a fabricating method and a fabricating apparatus foran electrode for a secondary battery of one embodiment of the presentinvention will be described with reference to FIG. 1 and FIGS. 3A to 3F.

FIG. 3A is a perspective view of an external body 11. A sheet made of aflexible base material is prepared as the exterior body 11. As thesheet, a stack, a metal film provided with an adhesive layer (alsoreferred to as a heat-seal layer) or sandwiched between adhesive layersis used. As the adhesive layer, a heat-seal resin film containing, e.g.,polypropylene or polyethylene is used. In this embodiment, a metalsheet, specifically, aluminum foil whose top surface is provided with anylon resin and whose bottom surface is provided with a stack includingan acid-proof polypropylene film and a polypropylene film is used as thesheet. The sheet is cut to prepare the film-like exterior body 11illustrated in FIG. 3A. The exterior body 11 is folded in half so thattwo end portions overlap each other, and is sealed on three sides withan adhesive layer.

The exterior body 11 is folded in half, whereby the state illustrated inFIG. 3A is produced.

FIG. 3B is a perspective view illustrating a positive electrode, aseparator 13, and a negative electrode that are stacked. The positiveelectrode includes at least a positive electrode current collector 12and a positive electrode active material layer 18. The negativeelectrode includes at least a negative electrode current collector 14and a negative electrode active material layer 19. Although the storagebattery electrodes (the positive electrode and the negative electrode)in the shape of rectangular sheets are shown in FIG. 3B, the shape ofthe storage battery electrodes is not limited thereto and can beselected from other given shapes as appropriate. The active materiallayer is formed over only one surface of the current collector; however,active material layers may be formed so that the current collector issandwiched therebetween. The active material layer is not necessarilyformed over an entire surface of the current collector, and an uncoatedregion such as a region for connection to an electrode tab is providedas appropriate.

There is no particular limitation on the positive electrode currentcollector and the negative electrode current collector as long as theyhave high conductivity without causing a significant chemical change ina secondary battery. For example, the current collectors can be formedusing a metal such as gold, platinum, iron, nickel, copper, aluminum,titanium, tantalum, or manganese, an alloy thereof (e.g., stainlesssteel). Furthermore, carbon, nickel, titanium, or the like can be usedas a coating material. Furthermore, silicon, neodymium, scandium,molybdenum, or the like may be added to improve heat resistance. Thecurrent collectors can have any of various shapes including a foil-likeshape, a sheet-like shape, a plate-like shape, a net-like shape, acylindrical shape, a coil shape, a punching-metal shape, anexpanded-metal shape, a porous shape, and a shape of non-woven fabric asappropriate. The current collectors may be formed to have microirregularities on the surfaces thereof in order to enhance adhesion toactive materials. The current collectors each preferably have athickness of more than or equal to 5 μm and less than or equal to 30 μm.

As the active material used in the positive electrode or the negativeelectrode, a material into and from which carrier ions such as lithiumions can be inserted and extracted is used. The average diameter ordiameter distribution of the active material particles can be controlledby crushing, granulation, and classification by an appropriate means.

Examples of positive electrode active materials that can be used for thepositive electrode active material layer 18 include a composite oxidewith an olivine structure, a composite oxide with a layered rock-saltstructure, and a composite oxide with a spinel structure. Specifically,a compound such as LiFeO₂, LiCoO₂, LiNiO₂, LiMn₂O₄, V₂O₅, Cr₂O₅, or MnO₂can be used.

Alternatively, a complex material (LiMPO₄ (general formula) (M is one ormore of Fe(II), Mn(II), Co(II), and Ni(II))) can be used. Typicalexamples of the general formula LiMPO₄ which can be used as a materialare lithium compounds such as LiFePO₄, LiNiPO₄, LiCoPO₄, LiMnPO₄,LiFe_(a)Ni_(b)PO₄, LiFe_(a)Co_(b)PO₄, LiFe_(a)Mn_(b)PO₄,LiNi_(a)Co_(b)PO₄, LiNi_(a)Mn_(b)PO₄ (a+b≤1, 0<a<1, and 0<b<1),LiFe_(c)Ni_(d)Co_(e)PO₄, LiFe_(c)Ni_(d)Mn_(e)PO₄,LiNi_(c)Co_(d)Mn_(e)PO₄ (c+d+e≤1, 0<c<1, 0<d<1, and 0<e<1), andLiFe_(f)Ni_(g)Co_(h)Mn_(i)PO₄ (f+g+h+i≤1, 0<f<1, 0<g<1, 0<h<1, and0<i<1).

Alternatively, a complex material such as Li_((2−j))MSiO₄ (generalformula) (M is one or more of Fe(II), Mn(II), Co(II), and Ni(II); 0≤j≤2)may be used. Typical examples of the general formula Li_((2−j))MSiO₄which can be used as a material are lithium compounds such asLi_((2−j))FeSiO₄, Li_((2—j))NiSiO₄, Li_((2−j))CoSiO₄, Li_((2−j))MnSiO₄,Li_((2−j))Fe_(k)Ni_(l)SiO₄, Li_((2−j))Fe_(k)Co_(l)SiO₄,Li_((2−j))Fe_(k)Mn_(l)SiO₄, Li_((2−j))Ni_(k)Co_(l)SiO₄,Li_((2−j))Ni_(k)Mn_(l)SiO₄ (k+l≤1, 0<k<1, and 0<l<1),Li_((2−j))Fe_(m)Ni_(n)Co_(q)SiO₄, Li_((2−j))Fe_(m)Ni_(n)Mn_(q)SiO₄,Li_((2−j))Ni_(m)Co_(n)Mn_(q)SiO₄ (m+n+q≤1, 0<m<1, 0<n<1, and 0<q<1), andLi_((2−j))Fe_(r)Ni_(s)Co_(t)Mn_(u)SiO₄ (r+s+t+u≤1, 0<r<1, 0<s<1, 0<t<1,and 0<u<1).

Still alternatively, a nasicon compound expressed by A_(x)M₂(XO₄)₃(general formula) (A=Li, Na, or Mg, M=Fe, Mn, Ti, V, Nb, or Al, X=S, P,Mo, W, As, or Si) can be used for the positive electrode activematerial. Examples of the nasicon compound are Fe₂(MnO₄)₃, Fe₂(SO₄)₃,and Li₃Fe₂(PO₄)₃. Further alternatively, for example, a compoundexpressed by Li₂MPO₄F, Li₂MP₂O₇, or Li₅MO₄ (general formula) (M=Fe orMn), a perovskite fluoride such as NaF₃ and FeF₃, a metal chalcogenide(a sulfide, a selenide, or a telluride) such as TiS₂ and MoS₂, an oxidewith an inverse spinel structure such as LiMVO₄, a vanadium oxide (V₂O₅,V₆O₁₃, LiV₃O₈, or the like), a manganese oxide, or an organic sulfurcompound can be used as the positive electrode active material.

In the case where carrier ions are alkali metal ions other than lithiumions, or alkaline-earth metal ions, a material containing an alkalimetal (e.g., sodium and potassium) or an alkaline-earth metal (e.g.,calcium, strontium, barium, beryllium, and magnesium) instead of lithiummay be used as the positive electrode active material.

As the separator 13, an insulator such as cellulose (paper),polyethylene with pores, and polypropylene with pores can be used.

As an electrolyte of an electrolytic solution, a material in whichcarrier ions can be transferred and which contains lithium ions servingas carrier ions is used. Typical examples of the electrolyte are lithiumsalts such as LiPF₆, LiClO₄, LiAsF₆, LiBF₄, LiCF₃SO₃, Li(CF₃SO₂)₂N, andLi(C₂F₅SO₂)₂N. One of these electrolytes may be used alone, or two ormore of them may be used in an appropriate combination and in anappropriate ratio.

As a solvent of the electrolytic solution, a material in which carrierions can be transferred is used. As the solvent of the electrolyticsolution, an aprotic organic solvent is preferably used. Typicalexamples of aprotic organic solvents include ethylene carbonate (EC),propylene carbonate, dimethyl carbonate, diethyl carbonate (DEC),γ-butyrolactone, acetonitrile, dimethoxyethane, tetrahydrofuran, and thelike, and one or more of these materials can be used. When a gelledhigh-molecular material is used as the solvent of the electrolyticsolution, safety against liquid leakage and the like is improved.Furthermore, the storage battery can be thinner and more lightweight.Typical examples of gelled high-molecular materials include a siliconegel, an acrylic gel, an acrylonitrile gel, a polyethylene oxide gel, apolypropylene oxide gel, a fluorine-based polymer gel, and the like.Alternatively, the use of one or more kinds of ionic liquids (roomtemperature molten salts) which have features of non-flammability andnon-volatility as a solvent of the electrolytic solution can prevent thestorage battery from exploding or catching fire even when the storagebattery internally shorts out or the internal temperature increasesowing to overcharging and others. An ionic liquid is a salt in the fluidstate and has high ion mobility (conductivity). An ionic liquid containsa cation and an anion. Examples of ionic liquids include an ionic liquidcontaining an ethylmethylimidazolium (EMI) cation and an ionic liquidcontaining an N-methyl-N-propylpiperidinium (PP₁₃) cation.

Instead of the electrolytic solution, a solid electrolyte including aninorganic material such as a sulfide-based inorganic material or anoxide-based inorganic material, or a solid electrolyte including ahigh-molecular material such as a polyethylene oxide (PEO)-basedhigh-molecular material may alternatively be used. When the solidelectrolyte is used, a separator and a spacer are not necessary.Furthermore, the battery can be entirely solidified; therefore, there isno possibility of liquid leakage and thus the safety of the battery isdramatically increased.

A material with which lithium can be dissolved and precipitated or amaterial into and from which lithium ions can be inserted and extractedcan be used for a negative electrode active material of the negativeelectrode active material layer 19; for example, lithium, a carbon-basedmaterial, an alloy-based material, or the like can be used.

Lithium is preferable because of its low redox potential (3.045 V lowerthan that of a standard hydrogen electrode) and a high specific capacityper unit weight and per unit volume (3860 mAh/g and 2062 mAh/cm³).

Examples of the carbon-based material include graphite, graphitizingcarbon (soft carbon), non-graphitizing carbon (hard carbon), a carbonnanotube, graphene, carbon black, and the like.

Examples of the graphite include artificial graphite such as meso-carbonmicrobeads (MCMB), coke-based artificial graphite, or pitch-basedartificial graphite and natural graphite such as spherical naturalgraphite.

Graphite has a low potential substantially equal to that of lithium (0.1V to 0.3 V vs. Li/Li⁺) when lithium ions are intercalated into thegraphite (while a lithium-graphite intercalation compound is formed).For this reason, a lithium-ion secondary battery can have a highoperating voltage. In addition, graphite is preferable because of itsadvantages such as a relatively high capacity per unit volume, smallvolume expansion, low cost, and safety greater than that of lithium.

For the negative electrode active material, an alloy-based material thatenables charge-discharge reactions by an alloying reaction and adealloying reaction with lithium can be used. In the case where carrierions are lithium ions, a material containing at least one of Al, Si, Ge,Sn, Pb, Sb, Bi, Ag, Au, Zn, Cd, In, Ga, and the like can be used as suchan alloy-based material, for example. Such elements have a highercapacity than carbon. In particular, silicon has a significantly hightheoretical capacity of 4200 mAh/g. For this reason, silicon ispreferably used as the negative electrode active material. Examples ofthe alloy-based material using such elements include Mg₂Si, Mg₂Ge,Mg₂Sn, SnS₂, V₂Sn₃, FeSn₂, CoSn₂, Ni₃Sn₂, Cu₆Sn₅, Ag₃Sn, Ag₃Sb, Ni₂MnSb,CeSb₃, LaSn₃, La₃Co₂Sn₇, CoSb₃, InSb, SbSn, and the like.

Alternatively, for the negative electrode active materials, an oxidesuch as SiO, SnO, SnO₂, titanium dioxide (TiO₂), lithium titanium oxide(Li₄Ti₅O₁₂), lithium-graphite intercalation compound (Li_(x)C₆), niobiumpentoxide (Nb₂O₅), tungsten oxide (WO₂), or molybdenum oxide (MoO₂) canbe used. Note that SiO refers to the powder of a silicon oxide includinga silicon-rich portion and can also be referred to as SiO_(y) (2>y>0).Examples of SiO include a material containing one or more of Si₂O₃,Si₃O₄, and Si₂O and a mixture of Si powder and silicon dioxide (SiO₂).Furthermore, SiO may contain another element (e.g., carbon, nitrogen,iron, aluminum, copper, titanium, calcium, and manganese). In otherwords, SiO refers to a colored material containing two or more of singlecrystal silicon, amorphous silicon, polycrystalline silicon, Si₂O₃,Si₃O₄, Si₂O, and SiO₂. Thus, SiO can be distinguished from SiO_(x) (x is2 or more), which is clear and colorless or white. Note that in the casewhere a secondary battery is fabricated using SiO as a material thereofand the SiO is oxidized because of repeated charge and discharge cycles,SiO is changed into SiO₂ in some cases.

Still alternatively, for the negative electrode active materials,Li_(3−x)M_(x)N (M=Co, Ni, or Cu) with a Li₃N structure, which is anitride containing lithium and a transition metal, can be used. Forexample, Li_(2.6)Co_(0.4)N₃ is preferable because of high charge anddischarge capacity (900 mAh/g and 1890 mAh/cm³).

A nitride containing lithium and a transition metal is preferably used,in which case lithium ions are contained in the negative electrodeactive materials and thus the negative electrode active materials can beused in combination with a material for a positive electrode activematerial that does not contain lithium ions, such as V₂O₅ or Cr₃O₈. Inthe case of using a material containing lithium ions as a positiveelectrode active material, the nitride containing lithium and atransition metal can be used for the negative electrode active materialby extracting the lithium ions contained in the positive electrodeactive material in advance.

Alternatively, a material that causes a conversion reaction can be usedfor the negative electrode active materials; for example, a transitionmetal oxide that does not cause an alloy reaction with lithium, such ascobalt oxide (CoO), nickel oxide (NiO), and iron oxide (FeO), may beused. Other examples of the material which causes a conversion reactioninclude oxides such as Fe₂O₃, CuO, Cu₂O, RuO₂, and Cr₂O₃, sulfides suchas CoS_(0.89), NiS, and CuS, nitrides such as Zn₃N₂, Cu₃N, and Ge₃N₄,phosphides such as NiP₂, FeP₂, and CoP₃, and fluorides such as FeF₃ andBiF₃. Note that any of the fluorides can be used as a positive electrodeactive material because of its high potential.

The negative electrode active material layer 19 may further include abinder for increasing adhesion of active materials, a conductiveadditive for increasing the conductivity of the negative electrodeactive material layer 19, and the like in addition to the above negativeelectrode active materials.

In the secondary battery, for example, the separator 13 has a thicknessof approximately 25 μm; the positive electrode current collector 12 hasa thickness of approximately 20 μm to 40 μm; the positive electrodeactive material layer 18 has a thickness of approximately 100 μm; thenegative electrode active material layer 19 has a thickness ofapproximately 100 μm; and the negative electrode current collector 14has a thickness of approximately 18 μm to 40 μm.

FIG. 1 is a schematic perspective view illustrating a fabricatingapparatus 1000. The fabricating apparatus 1000 includes a container1001, a cover 1002, an outlet 1003, a stirring means 1004, anintroduction tube 1005, an electrode 1006 to be treated, an electrode1007, a first cord 1008, a second cord 1009, and a control device 1010.

First, an electrolytic solution is introduced into the container in thefabricating apparatus illustrated in FIG. 1. A material with lowvolatility is preferably used as an electrolytic solution introducedinto the container. An electrolytic solution used in a secondary batteryis preferably different from that introduced into the container. As theelectrolytic solution used in the secondary battery, a material withwhich a highly stable film is deposited on a negative electrode is used.Note that as the electrolytic solution used in the container, a materialsubstantially the same as that to be used in the secondary battery maybe used. In addition, a current collector (sheet-like electrode) ofwhich one surface or both surfaces is/are provided with an activematerial layer (layers) is prepared, the cover 1002 is opened, and thesheet-like electrode that is rolled is put in the electrolytic solutionin the container 1001 in the fabricating apparatus.

The put current collector (electrode 1006 to be treated) is electricallyconnected to a load via a holding means (e.g., a conductive fastenersuch as a wiring clip). The holding means is electrically connected tothe control device 1010 via the first cord 1008.

The control device 1010 has at least two cord wirings. One of the cordwirings (the first cord 1008) is electrically connected to the currentcollector via the holding means, and the other cord wiring (the secondcord 1009) is electrically connected to metal foil or a metal plate. Inthis embodiment, lithium foil used as the electrode 1007 andelectrically connected to the other cord wiring is also put in theelectrolytic solution in the container. Alternatively, a platinumelectrode may be used instead of lithium foil as the electrode 1007.Still alternatively, a high-potential negative electrode of FePO₄, LTO,or the like that is predoped with lithium can be used as the electrode1007.

The electrolytic solution is provided between the two cord wirings ofthe control device 1010. The control device 1010 adjusts the amount ofcurrent and voltage that are supplied and applied to the electrolyticsolution provided between the two cord wirings, and the like to performoxidation or reduction on the active material layer placed in theelectrolytic solution.

Furthermore, the stirring means 1004 is provided in FIG. 1 to promote anelectrochemical reaction (oxidation or reduction) for shortening oftreatment time. The stirring means 1004 transfers an argon gas into theelectrolytic solution through the introduction tube 1005 with a pump andperforms stirring by utilizing formed bubbles. In the case of using anargon gas, the stirring means 1004 can be configured to make argon gasbubbles pass through a gap of the rolled electrode as well as to performstirring. In addition, in the case of using an argon gas, certaindistance is ensured between facing surfaces of the rolled electrode tofacilitate release of gas components (gases on a surface of theelectrode or bubbles in the electrolytic solution), such as a hydrogengas, a carbon monoxide gas, a carbon dioxide gas, and the like generatedas decomposition products of the electrolytic solution in the vicinityof the electrode and an oxygen gas, generated from the electrode, fromthe electrolytic solution.

An electrochemical reaction (oxidation or reduction) is caused while theelectrolytic solution is stirred. After the occurrence of theelectrochemical reaction, the electrode 1006 to be treated is taken outfrom the electrolytic solution in the container. Then, the electrode1006 to be treated is dried and processed into a desired shape, so thata positive electrode current collector or a negative electrode currentcollector is formed.

Next, a lead electrode 16 a and a lead electrode 16 b having sealinglayers 15 that are illustrated in FIG. 3C are prepared. The leadelectrode 16 a and the lead electrode 16 b are each also referred to asa lead terminal and provided in order to lead a positive electrode or anegative electrode of a secondary battery to the outside of the exteriorbody 11. The lead electrode 16 a is electrically connected to thepositive electrode. As a material for the lead electrode 16 a, amaterial that can be used for the positive electrode current collector,such as aluminum, can be used. The lead electrode 16 b is electricallyconnected to the negative electrode. As a material for the leadelectrode 16 b, a material that can be used for the negative electrodecurrent collector, such as copper, can be used.

Then, the lead electrode 16 a is electrically connected to a protrudingportion of the positive electrode current collector 12 by ultrasonicwelding or the like. The lead electrode 16 b is electrically connectedto a protruding portion of the negative electrode current collector 14by ultrasonic welding or the like.

Then, two sides of the exterior body 11 are sealed by thermocompressionbonding, and one side is left open for introduction of an electrolyticsolution. In thermocompression bonding, the sealing layers 15 providedover the lead electrodes are also melted, thereby fixing the leadelectrodes and the exterior body 11 to each other. After that, in areduced-pressure atmosphere or an inert atmosphere, a desired amount ofelectrolytic solution is introduced to the inside of the exterior body11 in the form of a bag.

A stack formed of a positive electrode, a separator 13, and a negativeelectrode is packed in a region surrounded by an exterior body 11 havingan opening, the electrolytic solution 20 is introduced into the regionsurrounded by the exterior body 11, and the opening of the exterior bodyis closed. To close the opening of the exterior body, lastly, the sideof the film that has not been subjected to thermocompression bonding andis left open is sealed by thermocompression bonding.

In this manner, a secondary battery 40 illustrated in FIG. 3D can befabricated. FIG. 3E illustrates a cross section along chain line A-B inFIG. 3D. An edge region indicated in FIG. 3D is athermocompression-bonded region 17.

As illustrated in FIG. 3E, an end portion of the secondary battery 40 issealed with an adhesive layer 30, and the other portion is provided withan electrolytic solution 20. The adhesive layer 30 is a solid obtainedin such a manner that part of the exterior body 11 is melted bythermocompression bonding and then cooled.

Here, a current flow in charging a secondary battery will be describedwith reference to FIG. 3F. When a secondary battery using lithium isregarded as a closed circuit, lithium ions transfer and a current flowsin the same direction. Note that in the secondary battery using lithium,an anode and a cathode change places in charge and discharge, and anoxidation reaction and a reduction reaction occur on the correspondingsides; hence, an electrode with a high redox potential is called apositive electrode and an electrode with a low redox potential is calleda negative electrode. For this reason, in this specification, thepositive electrode is referred to as a “positive electrode” and thenegative electrode is referred to as a “negative electrode” in all thecases where charge is performed, discharge is performed, a reverse pulsecurrent is supplied, and a charging current is supplied. The use of theterms “anode” and “cathode” related to an oxidation reaction and areduction reaction might cause confusion because the anode and thecathode change places at the time of charging and discharging. Thus, theterms “anode” and “cathode” are not used in this specification. If theterm “anode” or “cathode” is used, it should be mentioned that the anodeor the cathode is which of the one at the time of charging or the one atthe time of discharging and corresponds to which of a positive electrodeor a negative electrode.

Two terminals in FIG. 3F are connected to a charger, and a secondarybattery 40 is charged. As the charge of the secondary battery 40proceeds, a potential difference between electrodes increases. Thedirection of a flow of a charging current is the direction in which acurrent flows in FIG. 3F. That is, the current flows from one terminaloutside the secondary battery 40 to the positive electrode currentcollector 12, flows from the positive electrode current collector 12 tothe negative electrode current collector 14 in the secondary battery 40,and flows from the negative electrode current collector 14 to the otherterminal outside the secondary battery 40.

Although an example of a small battery used in a portable informationterminal or the like is described in this embodiment, one embodiment ofthe present invention is not particularly limited to this example.Application to a large battery provided in a vehicle or the like is alsopossible.

(Embodiment 2)

In this embodiment, an example of a fabricating apparatus different fromthat in Embodiment 1 in the positional relation of the stirring means1004, the electrode 1007, and the electrode 1006 to be treated, and thelike will be described. Note that in FIG. 2, components that are thesame as those in FIG. 1 described in Embodiment 1 are denoted by thecommon reference numerals.

FIG. 2 is a schematic cross-sectional view illustrating a fabricatingapparatus 1020 including the container 1001, the stirring means 1004,the electrode 1006 to be treated, the electrode 1007, a plasticcontainer 1012 in which the components are provided, the first cord1008, the second cord 1009, and the control device 1010.

In FIG. 2, a magnetic stirrer is used as the stirring means 1004, and adevice incorporated in a stand 1014 rotates the magnetic stirrer in thecontainer 1001. In addition, a heater 1011 is provided to heat anelectrolytic solution 1015 in the container.

The fabricating apparatus 1020 is configured to cause an electrochemicalreaction (oxidation or reduction) in a nitrogen atmosphere or an argonatmosphere.

In the case where a batch-type apparatus in which more than oneelectrode 1006 to be treated is put in the electrolytic solution 1015 tocause an electrochemical reaction is employed, a large container isused, and a set of the electrode 1007, the first cord 1008, the secondcord 1009, and the control device 1010 is prepared for each of theelectrodes 1006 to be treated. In that case, one electrolytic solution,one container, one heater, and one stirring means can be used for thebatch-type apparatus.

This embodiment can be freely combined with Embodiment 1. For example,bubbles may be generated by introducing an argon gas into theelectrolytic solution 1015 while rotating the magnetic stirrer put inthe container in the apparatus illustrated in FIG. 2. This can promotean electrochemical reaction, which enables short-time oxidationtreatment and reduction treatment.

(Embodiment 3)

FIG. 4A is an external view of a coin-type (single-layer flat type)storage battery, and FIG. 4B is a cross-sectional view thereof.

In a coin-type storage battery 300, a positive electrode can 301doubling as a positive electrode terminal and a negative electrode can302 doubling as a negative electrode terminal are insulated from eachother and sealed by a gasket 303 made of polypropylene or the like. Apositive electrode 304 includes a positive electrode current collector305 and a positive electrode active material layer 306 provided incontact with the positive electrode current collector 305. The positiveelectrode active material layer 306 may further include a binder forincreasing adhesion of positive electrode active materials, a conductiveadditive for increasing the conductivity of the positive electrodeactive material layer, and the like in addition to the active materials.As the conductive additive, a material that has a large specific surfacearea is preferably used; for example, acetylene black (AB) can be used.Alternatively, a carbon material such as a carbon nanotube, graphene, orfullerene can be used.

A negative electrode 307 includes a negative electrode current collector308 and a negative electrode active material layer 309 provided incontact with the negative electrode current collector 308. The negativeelectrode active material layer 309 may further include a binder forincreasing adhesion of negative electrode active materials, a conductiveadditive for increasing the conductivity of the negative electrodeactive material layer, and the like in addition to the negativeelectrode active materials. A separator 310 and an electrolyte (notillustrated) are provided between the positive electrode active materiallayer 306 and the negative electrode active material layer 309.

Any of the materials described in Embodiment 1 is used as a negativeelectrode active material in the negative electrode active materiallayer 309. Before a battery is assembled, oxidation treatment andreduction treatment are performed on the negative electrode 307 in anelectrolytic solution with the use of the apparatus described inEmbodiment 1 or 2.

Any of the materials for the current collectors that are described inEmbodiment 1 is used for the current collectors such as the positiveelectrode current collector 305 and the negative electrode currentcollector 308.

For the positive electrode active material layer 306, a material intoand from which lithium ions can be inserted and extracted can be used.For example, any of the materials for the positive electrode activematerial layer that are described in Embodiment 1 is used. Before abattery is assembled, oxidation treatment and reduction treatment areperformed on the positive electrode 304 in an electrolytic solution withthe use of the apparatus described in Embodiment 1 or 2.

As the separator 310, an insulator such as cellulose (paper),polyethylene, and polypropylene with pores can be used.

As an electrolyte of an electrolytic solution, a material that containscarrier ions is used. Typical examples of the electrolyte are lithiumsalts such as LiPF₆, LiClO₄, LiAsF₆, LiBF₄, LiCF₃SO₃, Li(CF₃SO₂)₂N, andLi(C₂F₅SO₂)₂N. One of these electrolytes may be used alone, or two ormore of them may be used in an appropriate combination and in anappropriate ratio.

Note that when carrier ions are alkali metal ions other than lithiumions, or alkaline-earth metal ions, instead of lithium in the abovelithium salts, an alkali metal (e.g., sodium and potassium), analkaline-earth metal (e.g., calcium, strontium, barium, beryllium, andmagnesium) may be used for the electrolyte.

As a solvent of the electrolytic solution, a material with the carrierion mobility is used. As the solvent of the electrolytic solution, anaprotic organic solvent is preferably used. Typical examples of aproticorganic solvents include EC, propylene carbonate, dimethyl carbonate,DEC, γ-butyrolactone, acetonitrile, dimethoxyethane, tetrahydrofuran,and the like, and one or more of these materials can be used. When agelled high-molecular material is used as the solvent of theelectrolytic solution, safety against liquid leakage and the like isimproved. Furthermore, the storage battery can be thinner and morelightweight. Typical examples of gelled high-molecular materials includea silicone gel, an acrylic gel, an acrylonitrile gel, a polyethyleneoxide gel, a polypropylene oxide gel, a fluorine-based polymer gel, andthe like. Alternatively, the use of one or more kinds of ionic liquids(room temperature molten salts) which have features of non-flammabilityand non-volatility as a solvent of the electrolytic solution can preventthe storage battery from exploding or catching fire even when thestorage battery internally shorts out or the internal temperatureincreases owing to overcharging and others.

For the positive electrode can 301 and the negative electrode can 302, ametal having a corrosion-resistant property to an electrolytic solution,such as nickel, aluminum, or titanium, an alloy of such a metal, or analloy of such a metal and another metal (e.g., stainless steel or thelike) can be used. Alternatively, the positive electrode can 301 and thenegative electrode can 302 are preferably covered with nickel, aluminum,or the like in order to prevent corrosion due to the electrolyticsolution. The positive electrode can 301 and the negative electrode can302 are electrically connected to the positive electrode 304 and thenegative electrode 307, respectively.

The negative electrode 307, the positive electrode 304, and theseparator 310 are immersed in the electrolytic solution. Then, asillustrated in FIG. 4B, the positive electrode 304, the separator 310,the negative electrode 307, and the negative electrode can 302 arestacked in this order with the positive electrode can 301 positioned atthe bottom, and the positive electrode can 301 and the negativeelectrode can 302 are subjected to pressure bonding with the gasket 303interposed therebetween. In such a manner, the coin-type storage battery300 can be manufactured.

FIG. 4C illustrates an example of a cylindrical storage battery. FIG. 4Cis a schematic cross-sectional view of the cylindrical storage battery.

The cylindrical storage battery 600 includes a positive electrode cap(battery cap) 601 and a battery can (outer can) 602. The positiveelectrode cap 601 and the battery can 602 are insulated from each otherby a gasket (insulating gasket) 610.

FIG. 4C is a diagram schematically illustrating a cross section of thecylindrical storage battery. Inside the battery can 602 having a hollowcylindrical shape, a battery element in which a strip-like positiveelectrode 604 and a strip-like negative electrode 606 are wound with astripe-like separator 605 interposed therebetween is provided. Althoughnot illustrated, the battery element is wound around a center pin. Oneend of the battery can 602 is close and the other end thereof is open.For the battery can 602, a metal having a corrosion-resistant propertyto an electrolytic solution, such as nickel, aluminum, or titanium, analloy of such a metal, or an alloy of such a metal and another metal(e.g., stainless steel or the like) can be used. Alternatively, thebattery can 602 is preferably covered with nickel, aluminum, or the likein order to prevent corrosion due to the electrolytic solution. Insidethe battery can 602, the battery element in which the positiveelectrode, the negative electrode, and the separator are wound isprovided between a pair of insulating plates 608 and 609 that face eachother. Furthermore, a nonaqueous electrolytic solution (not illustrated)is injected inside the battery can 602 provided with the batteryelement. As the nonaqueous electrolytic solution, a nonaqueouselectrolytic solution that is similar to those of the coin-type storagebattery and a laminate storage battery can be used.

Although the positive electrode 604 and the negative electrode 606 canbe formed in a manner similar to that of the positive electrode and thenegative electrode of the coin-type storage battery described above, thedifference lies in that, since the positive electrode and the negativeelectrode of the cylindrical storage battery are wound, active materialsare formed on both sides of the current collectors. A positive electrodeterminal (positive electrode current collecting lead) 603 is connectedto the positive electrode 604, and a negative electrode terminal(negative electrode current collecting lead) 607 is connected to thenegative electrode 606. Both the positive electrode terminal 603 and thenegative electrode terminal 607 can be formed using a metal materialsuch as aluminum. The positive electrode terminal 603 and the negativeelectrode terminal 607 are resistance-welded to a safety valve mechanism612 and the bottom of the battery can 602, respectively. The safetyvalve mechanism 612 is electrically connected to the positive electrodecap 601 through a positive temperature coefficient (PTC) element 611.The safety valve mechanism 612 cuts off electrical connection betweenthe positive electrode cap 601 and the positive electrode 604 when theinternal pressure of the battery exceeds a predetermined thresholdvalue. The PTC element 611, which serves as a thermally sensitiveresistor whose resistance increases as temperature rises, limits theamount of current by increasing the resistance, in order to preventabnormal heat generation. Note that barium titanate (BaTiO₃)-basedsemiconductor ceramic can be used for the PTC element.

Note that in this embodiment, the coin-type storage battery and thecylindrical storage battery are given as examples of the storagebattery; however, any of storage batteries with a variety of shapes,such as a sealed storage battery and a square-type storage battery, canbe used. Furthermore, a structure in which a plurality of positiveelectrodes, a plurality of negative electrodes, and a plurality ofseparators are stacked or wound may be employed.

This embodiment can be combined with Embodiment 1 or 2.

EXAMPLE 1

In this example, a treatment apparatus illustrated in FIG. 6 wasfabricated based on an apparatus design conceptual diagram in FIG. 5.Results obtained by modifying an electrode using the treatment apparatusin FIG. 6 will be described below.

FIG. 5 is the conceptual diagram of the treatment apparatus. Anelectrolytic solution 215 is introduced into a container 202, andlithium 207, a separator 206 that surrounds the lithium 207, and a metalfilm 208 serving as a current collector between the separator 206 andthe container 202 are further positioned. Note that the metal film 208is provided with a positive electrode active material layer or anegative electrode active material layer.

As illustrated in FIG. 5, a potential difference is generated betweenthe lithium 207 and the metal film 208 to apply a load to the positiveelectrode active material layer or the negative electrode activematerial layer, whereby the active material layer is modified ordegassed.

FIG. 6 is a photograph of an actually fabricated treatment apparatusthat is seen from above the container. Components in FIG. 6 that are thesame as those in FIG. 5 are denoted by the common reference numerals.Note that in FIG. 6, lithium in the form of metal foil is connected to aload using a wiring clip 230. The separator 206 is provided so as tosurround the metal foil. The metal film 208 is connected to a load usinga wiring clip 231 outside the container 202.

As a comparative example, a coin-type half cell using SiO, which is amaterial with low initial charge and discharge efficiency, as a negativeelectrode active material was fabricated, and the initial charge anddischarge efficiency thereof was measured to be 71%.

Note that SiO refers to the powder of a silicon oxide including asilicon-rich portion and can also be referred to as SiO_(y) (2>y>0).Examples of SiO include a material containing one or more of Si₂O₃,Si₃O₄, and Si₂O and a mixture of Si powder and silicon dioxide (SiO₂).Furthermore, SiO may contain another element (e.g., carbon, nitrogen,iron, aluminum, copper, titanium, calcium, and manganese). In otherwords, SiO refers to a colored material containing two or more of singlecrystal silicon, amorphous silicon, polycrystalline silicon, Si₂O₃,Si₃O₄, Si₂O, and SiO₂. Thus, SiO can be distinguished from SiO_(x) (x is2 or more), which is clear and colorless or white. Note that in the casewhere a secondary battery is fabricated using SiO as a material thereofand the SiO is oxidized because of repeated charge and discharge cycles,SiO is changed into SiO₂ in some cases.

The half cell includes lithium foil as one electrode, polypropylene andglass fiber filter paper as a separator, and an electrolytic solutioncontaining LiPF₆ as a salt and a mixed solvent containing ethylenecarbonate and diethylene carbonate at a ratio of 3:7, which is anaprotic organic solvent.

The conditions for measurement of the charge and dischargecharacteristics of the half cell at room temperature (25° C.) wereconstant current/constant voltage (CCCV) discharge (0.2 C, 0.01 V, theminimum value: 0.01 C) and constant current (CC) charge (0.2 C, 1.5 V).

A sample including a negative electrode active material layer thatcontained SiO as a negative electrode active material and was formedover a metal film serving as a current collector was subjected totreatment using the treatment apparatus illustrated in FIG. 6 so that afilm containing Li₄SiO₄ was formed on the surface of the negativeelectrode active material. The condition for treatment using thetreatment apparatus was CCCV discharge (0.05 C, 0.4 V, the maximumvalue: 700 mAh/g). The initial charge and discharge efficiency of thesample half cell was measured to be 90%.

It was found from these results that the sample previously subjected totreatment using the treatment apparatus in FIG. 6 (the initial chargeand discharge capacity: 90%) was more excellent than the comparativesample not subjected to treatment using the treatment apparatus in FIG.6 (the initial charge and discharge capacity: 71%).

The initial charge and discharge efficiency refers to the ratio of theinitial discharge capacity to the initial charge capacity. The initialdischarge capacity refers to discharge capacity in the initial chargeand discharge cycle. The initial charge and discharge efficiency (%) isthe proportion of electric power capacity (Ahr) at the time of dischargeto electric power capacity at the time of charge. Here, the initialcharge and discharge efficiency is calculated from the charge anddischarge curves obtained in the case where constant current dischargeis performed until the voltage falls to 0.01 V, the constant-voltagestate is maintained at 0.01 V until the current value becomes less than0.01 C, the half cell is left in the open-circuit state for an hour, andthen the half cell is discharged.

EXAMPLE 2

In this example, a current collector provided with a positive electrodeactive material was subjected to treatment using the apparatusillustrated in FIG. 6 instead of the current collector provided with thenegative electrode active material that is described in Example 1, sothat the positive electrode active material was modified. The obtainedresults will be described below.

A lithium-manganese composite oxide that is represented by a compositionformula Li_(a)Mn_(b)M_(c)O_(d) was used as the positive electrode activematerial. In this example, a lithium-manganese composite oxiderepresented by a composition formula Li_(1.68)Mn_(0.8062)Ni_(0.318)O₃refers to that formed at a ratio (molar ratio) of the amounts of rawmaterials of Li₂CO₃: MnCO₃: NiO=0.84:0.8062:0.318. Although thislithium-manganese composite oxide is represented by the compositionformula Li_(1.68)Mn_(0.8062)Ni_(0.318)O₃, the composition might bedifferent. The lithium-manganese composite oxide was coated with carbon.The thickness of a layer containing the carbon is preferably greaterthan or equal to 0.4 nm and less than or equal to 40 nm.

Furthermore, the average size of primary particles of thelithium-manganese composite oxide is preferably greater than or equal to5 nm and less than or equal to 50 μm, more preferably greater than orequal to 100 nm and less than or equal to 500 nm, for example.Furthermore, the specific surface area is preferably greater than orequal to 5 m²/g and less than or equal to 15 m²/g. Furthermore, theaverage size of secondary particles is preferably greater than or equalto 5 μm and less than or equal to 50 μm. Note that the average particlesizes can be measured with a particle size distribution analyzer or thelike using a laser diffraction and scattering method or by observationwith a scanning electron microscope (SEM) or a TEM. The specific surfacearea can be measured by a gas adsorption method.

The current collector provided with the positive electrode activematerial was subjected to treatment using the apparatus illustrated inFIG. 6 so as to be degassed, which suppresses generation of a gas afterfabrication of a secondary battery. The conditions for treatment usingthe treatment apparatus were CCCV charge (0.1 C, 4.8 V, the minimumvalue: 0.01 C) and CCCV discharge (0.1 C, 2 V, the minimum value: 0.01C).

The half cell includes lithium foil as one electrode, polypropylene as aseparator, and an electrolytic solution containing LiPF₆ as a salt and amixed solvent of ethylene carbonate and diethylene carbonate, which isan aprotic organic solvent.

The conditions for measurement of the charge and dischargecharacteristics of the half cell at room temperature (25° C.) were CCcharging (0.1 C and 4.8 V) and CC discharging (0.1 C and 2.0 V).

FIG. 7A shows the charge and discharge characteristics. The solid lineand the dashed line indicate initial charge and dischargecharacteristics and second charge and discharge characteristics,respectively. FIG. 7A shows that irreversible capacity exists in initialcharge and discharge. The horizontal axis represents capacity (mAh/g).

Table 1 shows measurement results of charge and discharge efficiency.

TABLE 1 charge and charge capacity discharge capacity dischargeefficiency Cycle [mAh/g] [mAh/g] [%] 1 277.7 262.9 94.7 2 265.0 262.999.2

As shown in Table 1, the initial charge and discharge efficiency was94.7%.

In addition, a sample not subjected to treatment using the apparatusillustrated in FIG. 6 was fabricated as a comparative example, and thecharge and discharge characteristics were measured. FIG. 7B shows themeasurement results.

Table 2 shows measurement results of the charge and discharge efficiencyof the comparative example.

TABLE 2 Comparative Example charge and charge capacity dischargecapacity discharge efficiency Cycle [mAh/g] [mAh/g] [%] 1 287.3 261.791.1 2 281.4 278.1 98.8

As shown in Table 2, the initial charge and discharge efficiency of thecomparative example was 91.1%.

These results indicate that the use of the apparatus illustrated in FIG.6 can improve the initial charge and discharge efficiency, reducing lossof capacity. Moreover, the charge and discharge efficiency in the secondand later cycles can also be improved.

EXAMPLE 3

In this example, evaluation results of the charge and dischargecharacteristics of the secondary batteries fabricated in Examples 1 and2 will be described.

First, CC charging, CCCV charging, and CC discharging will be described.

<CC Charging>

CC charging will be described. CC charging is a charging method in whicha constant current is made to flow to a secondary battery in the wholecharging period and charging is terminated when the voltage reaches apredetermined voltage. The secondary battery is assumed to be expressedby an equivalent circuit with internal resistance R and secondarybattery capacitance C as illustrated in FIG. 8A. In this case, asecondary battery voltage V_(B) is the sum of a voltage V_(R) applied tothe internal resistance R and a voltage V_(C) applied to the secondarybattery capacitance C.

While the CC charging is performed, a switch is on as illustrated inFIG. 8A, so that a constant current I flows to the secondary battery.During the period, the current I is constant; thus, according to theOhm's law (V_(R)=R×I), the voltage V_(R) applied to the internalresistance R is also constant. In contrast, the voltage V_(C) applied tothe secondary battery capacitance C increases over time. Accordingly,the secondary battery voltage V_(B) increases over time.

When the secondary battery voltage V_(B) reaches a predeterminedvoltage, e.g., 4.1 V, the charging is terminated. On termination of theCC charging, the switch is turned off as illustrated in FIG. 8B, and thecurrent I becomes 0. Thus, the voltage V_(R) applied to the internalresistance R becomes 0 V. Consequently, the secondary battery voltageV_(B) is decreased by the lost voltage drop in the internal resistanceR.

FIG. 8C shows an example of the secondary battery voltage V_(B) andcharging current while the CC charging is performed and after the CCcharging is terminated. The secondary battery voltage V_(B) increaseswhile the CC charging is performed, and slightly decreases after the CCcharging is terminated.

<CCCV Charging>

Next, CCCV charging will be described. CCCV charging is a chargingmethod in which CC charging is performed until the voltage reaches apredetermined voltage and then CV (constant voltage) charging isperformed until the amount of current flow becomes small, specifically,a termination current value.

While the CC charging is performed, a switch of a constant current powersource is on and a switch of a constant voltage power source is off asillustrated in FIG. 9A, so that the constant current I flows to asecondary battery. During the period, the current I is constant; thus,according to the Ohm's law (V_(R)=R×I), the voltage V_(R) applied to theinternal resistance R is also constant. In contrast, the voltage V_(C)applied to the secondary battery capacitance C increases over time.Accordingly, the secondary battery voltage V_(B) increases over time.

When the secondary battery voltage V_(B) reaches a predeterminedvoltage, e.g., 4.1 V, switching is performed from the CC charging to theCV charging. While the CV charging is performed, the switch of theconstant voltage power source is on and the switch of the constantcurrent power source is off as illustrated in FIG. 9B; thus, thesecondary battery voltage V_(B) is constant. In contrast, the voltageV_(C) applied to the secondary battery capacitance C increases overtime. Since V_(B)=V_(R)+V_(C) is satisfied, the voltage V_(R) applied tothe internal resistance R decreases over time. As the voltage V_(R)applied to the internal resistance R decreases, the current I flowing tothe secondary battery also decreases according to the Ohm's law(V_(R)=R×I).

When the current I flowing to the secondary battery becomes apredetermined current, e.g., approximately 0.01 C, charging isterminated. On termination of the CCCV charging, all the switches areturned off as illustrated in FIG. 9C, so that the current I becomes 0.Accordingly, the voltage V_(R) applied to the internal resistance Rbecomes 0 V. However, the voltage V_(R) applied to the internalresistance R becomes sufficiently small by the CV charging; thus, evenwhen a voltage drop no longer occurs in the internal resistance R, thesecondary battery voltage V_(B) hardly decreases.

FIG. 9D shows an example of the secondary battery voltage V_(B) andcharging current while the CCCV charging is performed and after the CCCVcharging is terminated. Even after the CCCV charging is terminated, thesecondary battery voltage V_(B) hardly decreases.

<CC Discharging>

Next, CC discharging will be described. CC discharging is a dischargingmethod in which a constant current is made to flow from a secondarybattery in the whole discharging period and discharging is ended whenthe secondary battery voltage V_(B) reaches a predetermined voltage,e.g., 2.5 V.

FIG. 10 shows an example of the secondary battery voltage V_(B) andcharging current while the CC discharging is performed. As dischargingproceeds, the secondary battery voltage V_(B) decreases.

Next, a charge rate and a discharge rate will be described. Thedischarge rate refers to the relative ratio of discharging current tobattery capacity and is expressed in a unit C. A current ofapproximately 1 C in a battery with a rated capacity X (Ah) is X A. Thecase where discharging is performed at a current of 2X A is rephrased asfollows: discharging is performed at 2 C. The case where discharging isperformed at a current of X/5 A is rephrased as follows: discharging isperformed at 0.2 C. Similarly, a charge rate of 1 C indicates a currentvalue at which a battery can be completely charged in just 1 hour by CCcharging.

This application is based on Japanese Patent Application serial no.2014-138755 filed with Japan Patent Office on Jul. 4, 2014, the entirecontents of which are hereby incorporated by reference.

What is claimed is:
 1. A fabricating method for a secondary battery,comprising: forming a first electrode including a positive electrodeactive material layer; forming a second electrode including a negativeelectrode active material layer; rolling the second electrode; providingthe rolled second electrode into a first electrolytic solution, therolled second electrode provided over a third electrode comprisinglithium; performing an electrochemical reaction to the second electrodewith the third electrode in the first electrolytic solution; packing astack including the first electrode and the second electrode in anexterior body having an opening; introducing a second electrolyticsolution in the exterior body; and closing the opening of the exteriorbody, wherein a stirring unit having discotic shape is provided betweenthe third electrode and the rolled second electrode, wherein argon gasbubbles output from the stirring unit pass through a gap of the rolledsecond electrode in the electrochemical reaction, and wherein at leastone of the first electrolytic solution and the second electrolyticsolution contains lithium.
 2. The fabricating method for a secondarybattery, according to claim 1, further comprising the step of: takingout the second electrode from the first electrolytic solution afterperforming the electrochemical reaction.
 3. The fabricating method for asecondary battery, according to claim 2, further comprising the step of:drying the second electrode after taking out the first electrode fromthe first electrolytic solution.
 4. The fabricating method for asecondary battery, according to claim 1, wherein lithium foil is used asthe third electrode when performing the electrochemical reaction.
 5. Thefabricating method for a secondary battery, according to claim 1,wherein the first electrolytic solution is stirred when performing theelectrochemical reaction.
 6. The fabricating method for a secondarybattery, according to claim 1, wherein the first electrolytic solutionis heated when performing the electrochemical reaction.
 7. Thefabricating method for a secondary battery, according to claim 1,wherein the first electrolytic solution comprises an ionic liquid. 8.The fabricating method for a secondary battery, according to claim 1,wherein the electrochemical reaction is performed at a pressure ofapproximately 0.5 atmospheres.
 9. The fabricating method for a secondarybattery, according to claim 1, wherein at least one of the firstelectrolytic solution and the second electrolytic solution comprisesLiPF₆, ethylene carbonate and diethylene carbonate.
 10. The fabricatingmethod for a secondary battery, according to claim 1, wherein thelithium is Li(CF₃SO₂)₂N.
 11. A fabricating method for a secondarybattery comprising: forming a first electrode including a positiveelectrode active material layer; forming a second electrode including anegative electrode active material layer comprising silicon; rolling thesecond electrode; providing the rolled second electrode into a firstelectrolytic solution, the rolled second electrode provided over a thirdelectrode comprising lithium; performing an electrochemical reaction tothe second electrode with the third electrode in the first electrolyticsolution; packing a stack including the first electrode and the secondelectrode in an exterior body having an opening; introducing a secondelectrolytic solution in the exterior body; and closing the opening ofthe exterior body, wherein a stirring unit having discotic shape isprovided between the third electrode and the rolled second electrode,wherein argon gas bubbles output from the stirring unit pass through agap of the rolled second electrode in the electrochemical reaction, andwherein at least one of the first electrolytic solution and the secondelectrolytic solution contains lithium.
 12. The fabricating method for asecondary battery, according to claim 11, further comprising the stepof: taking out the second electrode from the first electrolytic solutionafter performing the electrochemical reaction.
 13. The fabricatingmethod for a secondary battery, according to claim 12, furthercomprising the step of: drying the second electrode after taking out thefirst electrode from the first electrolytic solution.
 14. Thefabricating method for a secondary battery, according to claim 11,wherein lithium foil is used as the third electrode when performing theelectrochemical reaction.
 15. The fabricating method for a secondarybattery, according to claim 11, wherein the first electrolytic solutionis stirred when performing the electrochemical reaction.
 16. Thefabricating method for a secondary battery, according to claim 11,wherein the first electrolytic solution is heated when performing theelectrochemical reaction.
 17. The fabricating method for a secondarybattery, according to claim 11, wherein the first electrolytic solutioncomprises an ionic liquid.
 18. The fabricating method for a secondarybattery, according to claim 11, wherein the electrochemical reaction isperformed at a pressure of approximately 0.5 atmospheres.
 19. Thefabricating method for a secondary battery, according to claim 11,wherein at least one of the first electrolytic solution and the secondelectrolytic solution comprises LiPF₆, ethylene carbonate and diethylenecarbonate.
 20. The fabricating method for a secondary battery, accordingto claim 11, wherein the lithium is Li(CF₃SO₂)₂N.